In search of common sense: Salt intake, heart health and death

The FDA’s new recommended maximum for sodium intake is 2,300 milligrams per day. The American Heart Association recommends an even lower amount, 1,500 milligrams.

The FDA’s new recommended maximum for sodium intake is 2,300 milligrams per day. The American Heart Association recommends an even lower amount, 1,500 milligrams.

(Mario Tama, Getty Images)

Faye FlamBloomberg View

Here’s a salt paradox.

On the one hand you have Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention declaring in the Journal of the American Medical Association that reducing salt consumption will save hundreds of thousands of lives, and warning that 90 percent of Americans eat too much of it.

But then there are the epidemiologists whose research appears to point in the other direction. They track the connection between salt and deaths from heart attacks and strokes, and their studies indicate that while heavy salt eaters did die sooner, there is little evident danger from the average American’s intake. That’s usually expressed as 3,400 grams of sodium per day, which is roughly the amount in a teaspoon and a half of salt. (Salt and sodium intake are proportional, since salt is the primary source of dietary sodium.)

Salt is not a rising health scourge. U.S. salt consumption has been holding steady for decades, and is about the same as the global average.

The paradox has a solution, which is that salt is safe within a range. It’s reasonable to predict that lowering the average recommended intake will pull many people at the high end into a healthier range. And so lives may indeed be saved thanks to the U.S. Food and Drug Administration’s new guidelines, released last week and aimed mainly at reducing sodium in packaged foods and restaurant meals.

What’s not yet established is whether everybody else needs to cut back, or how much. The FDA’s new recommended maximum is 2,300 milligrams per day. The American Heart Association recommends an even lower amount, 1,500 milligrams, though that position is becoming increasingly untenable.

A few years ago, the Institute of Medicine put together a panel to assess the available evidence. It found none in favor of recommending consumption of less than 2,300 milligrams a day. There were even hints in the data that eating less might be harmful.

Rutgers University professor of medicine Brian Strom, who headed the panel, has told me in several previous interviews that the basis of the Heart Association’s recommendation is “not entirely rational.”

What it is, in effect, is a zero-tolerance policy. That’s because 1,500 milligrams is the minimum amount of sodium it’s possible to consume while eating enough food to sustain yourself. That is, if you eat nothing with added salt, you’ll still get about 1,500 milligrams from the sodium that occurs naturally in edible plants and animals.

Zero tolerance of salt comes from a counterproductive level of caution. It starts with a real scientific observation that eating a lot of salt raises blood pressure and poses a danger to people with hypertension. Then it takes a leap of logic by assuming that if less sodium is good for those folks, then the less the better for everyone.

But salt isn’t a dietary evil. The need for salt is embedded deep in human biochemistry. Salt in the bloodstream separates into charged ions — the basis of cellular energy storage and the drivers of the complex circuitry of the nervous system. With salt playing such an important role, it makes sense that too little or too much will kill us.

The question is where that healthy range lies. The medical community’s traditional recommendations came out of an exclusive focus on blood pressure. But a surprise came when researchers started to look instead at overall cardiovascular health. A 2014 study that tried to link salt consumption directly to death from heart disease and stroke, for example, showed that the lowest death rate occurred for people who consumed between 3,000 and 6,000 milligrams a day. That would put the average American’s consumption pattern in a safe range.

Nobody should change his or her behavior based on a single study, but other studies have also found the lowest death rate in a similar middle range.

Given the dangers of high blood pressure, it seems surprising that people didn’t start dying until they got up to the high intake of 6,000 milligrams a day. Professor Michael Alderman of the Albert Einstein College of Medicine has pointed out that other factors, including genes, stress and obesity can contribute to a breakdown in the body’s ability to maintain normal blood pressure. Salty food may exacerbate the problem without having been the primary cause.

He also questions the assumption that no possible harm can come from a very-low-salt diet. Some studies have hinted that such diets might raise triglyceride — a risk factor for heart disease. Nutrition researcher David McCarron is quoted in The New York Times saying that going below 3,000 milligrams is “dangerous.”

Strom, who headed the Institute of Medicine panel, doesn’t buy this. He has pointed out that in the study showing a higher death rate among those eating the least salt, it may not have been the lack of salt that caused the deaths. Instead, people in that group may be eating very-low-sodium diets because they have been diagnosed with health problems, or simply eating less food altogether because they are sick. He told me that he consumes about 2,300 milligrams because he’s lucky enough to have a spouse who cooks.

It’s perfectly reasonable that there’s some leeway in the healthy range — that evolution would have made it possible for people to thrive without being perfect. There may also be substantial individual differences in that safe range.

The good news is that FDA’s guidelines are unlikely to cause any harm to consumers. The proposal would encourage the food industry to tone down those heavily salted soups, chips, baked goods, salads and the like. That change won’t put anyone in danger of salt deficiency.

Whether such changes will reduce the pleasure of eating is a matter of taste. Some people think salty processed and fast food is delicious. I’d argue that homemade food is delicious — unless someone adds too much salt.

Bloomberg

Faye Flam writes about science, mathematics and medicine. She has been a staff writer for Science magazine and is the author of “The Score: How the Quest for Sex has Shaped the Modern Man.”